 planning and preservation. And it's a great honor for us to welcome today Professor Mathias Stirlich to our Historic Preservation Lecture Series. Professor Stirlich is Professor of Analytical Chemistry at the University of Ljubljana and Professor of Heritage Science at University College London and Senior Research Fellow at the Smithsonian Institutions Museum Conservation Institute. He's a chemist by training and an accredited conservator. His main research interests are the development of heritage science infrastructure, including instrumentation and methodology, as well as modeling of heritage materials, environments, values, and decision-making. And in particular, this question of environments is very interesting because we have followed his work over the years. He's really been a pioneer in challenging the notion that there is an object and a subject and nothing in between. And he's really made it very apparent that this environment is physical, is real, that connects subjects and objects. And he's done so by focusing in particular on smell, on the fact that the air is full of invisible materials that have an aesthetic quality to them and that we perceive those aesthetic qualities through our nose, sometimes through our eyes as well when the sun hits it right and there's enough dust in it, you can see it, but mostly through our nose. And he has really over the years carved a space for thinking about preservation through smell. And there, of course, has connected that to the question of values and emotions and how smell connects us to place by creating those psychological attachments to place. So he is an unusual scientist in the sense that he thinks both very analytically and also very aesthetically and is able to bridge the analytical and the emotional in his work and understand how technology and culture affect each other. He is a fellow of the Royal Society of Chemistry and the International Institute for Conservation. And in 2015, he received the Ambassador of Science of the Republic of Slovenia Award for the outstanding achievements in science and international collaboration. So it is a great honor and a great pleasure to welcome Professor Mathias Stirlich to Columbia University, albeit virtually. And since we cannot all clap together, I will do the clapping alone for everyone to give him a warm reception to our school. So Professor Stirlich, I hand the podium over to you. Thank you so much, Jorge. And I'm so pleased that you called me an unusual scientist. And I will definitely use that in how I introduce myself in the future. It's an enormous pleasure to be with you today. And I'm really, really happy and delighted and honored to have been invited. So thank you so much for having me. I'll talk, as Jorge already introduced, I'll talk a little bit about smells in museums or smells as heritage, if you like. And I'll consider three main aspects of how smells are considered in the conservation discourse. Smells are often seen as unwanted, as risks, even. Sometimes they're seen as a source of information about an object. And sometimes, and increasingly so, I think, they're seen as a piece of heritage, or perhaps even as a form or typology of heritage in and of itself. And that's how I'm going to structure the talk today. I hope that the few graphs and data points that I show are not going to be seen too difficult or in any way superfluous. But please do ask any questions at the end, because I'm really, really looking forward to our discussion as well. But before that, I'd like to introduce the institution where I spent most of the time working on these interesting research questions. As Jorge already introduced, I work as full-time professor of, I worked as full-time professor of heritage science at University College London, which is, as we just found out in our chat with Jorge, very similar to Columbia, both in terms of size and in terms of the variety of subjects that are being called. It's a particularly international university, and it is an absolutely interdisciplinary university. And I've been incredibly lucky to have worked at this institution for the past, well, 13 years, because without the drive to do interdisciplinary research and in collaboration between various faculties, I'm sure that a lot of what I'm going to talk about wouldn't have been possible. So I'm really, really grateful to a number of researchers and PhD students and graduate students that I've had the pleasure of working with in the past 14 years or so. The other aspect that makes UCL so special is the fact that it is situated in central London, and it sits among some world-leading and biggest heritage institutions that we also work with very often and collaborate with continuously. For example, the British Museum or the British Library, with whom we had one of the first projects focusing on heritage smells funded by the UK Science and Heritage Program, probably about eight years ago now, and then English Heritage or the VNA at the bottom with whom we've done a lot of work looking at preventive conservation, the role of pollution and similar in the past decade. And a lot of this research has been shaped by our students as well. And we've established a successful program, MRES program in Heritage Science in 2010, which then transformed into an MRES study and a doctoral training center in science and engineering and arts heritage and archaeology, which I led for a while. And this is our small group of 40 plus PhD students working on various aspects of science and heritage. And among them is Cecilia Vemibre, a student who joined us from Argentina, and as a communication specialist and specifically interested in smells as a form of heritage, specifically interested in how smells should be documented, how they should be valued and potentially conserved. So a lot of the presentation today has been influenced by our ongoing conversations into the value of smell as a communication tool, as well as the value of smell as a perhaps a form of heritage on its own. So as I promised, I'll focus on three specific aspects of smell in terms of heritage preservation. Very traditionally, smell or the volatile organic compounds of which smell is typically consists in indoor environments represents a risk in heritage environments. There is quite a lot of literature on this topic, and I'm not going to go into that at all. But I'll just consider whether it is really, really necessary to consider volatile organic compounds as a risk at any concentration. If it isn't, then, and hopefully I'll convince you that it isn't, I'll focus on volatile organic compounds or smells, if you like, as a source of information about objects. And that's how really my journey into smells as a form of heritage started. I really got interested in smells as perceived by conservators and sometimes used by conservators to judge the condition of objects. I very often watched conservators smelling objects and saying, this one is really degraded or that one must contain a lot of lignin. And through that, I started thinking if conservators can smell out objects that seem to be more degraded, then surely we could develop tools, analytical tools, perhaps, that will enable us to do that a little bit more accurately. And then as we did this travel, we started thinking that in many environments, smells are used as a way to communicate heritage to visitors. And when we did an environmental assessment study at the St. Paul's Cathedral, specifically at the Wren, incredibly historic and beautiful library, Wren Library in St. Paul's Cathedral in central London, the curator, the chief curator said that while he'd be happy for us to propose any number of preventive conservation measures, he would really like to keep the smell of the library because he felt that that was one of the key values of that library to visitors. And that really made me think that there is more to smell than just a mixture of volatile organic compounds. So looking at volatile organic compounds or smells more generally, as a source of conservation risk, there's a number of pieces of literature available. And I'm just going to quote one, the recent specification for managing environmental conditions for cultural collections that I helped to pull together as well. And towards the end of this document, there is a there's a small table that lists some of the acceptable thresholds for chemical pollutants in indoor air surrounding heritage collections. The three pollutants that are typically part of smell bouquets, if you like, are acetic acid, formic acid and formaldehyde. And those can be perceived at high enough concentrations by the human nose as well. Acetic acid has a typical vinegar smell and certain aldehydes, if not formaldehyde, have very typical smells as well. For example, of dry grass and some higher aldehydes, also of ripening fruit, for example. So it seemed to me that these are the concentrations quoted in this table and measured and assessed by numerous conservators were potentially in a high enough concentration to be smelled by humans. And if contained at smaller concentrations, then surely there is a sweet spot in terms of how high these concentrations could be allowed in an indoor atmosphere, that it wouldn't lead to an excessive risk and still be perceivable by the human nose. So we started doing a little bit of an experiment, a small experiment, looking at what concentrations of these compounds can still be admitted in the air, for example in archives or libraries, staying with the library theme. And of course, at very high concentrations, such as, for example, at the back of this framed photograph that was in close contact with the wooden board, at such high concentrations, obviously, those volatile acids and other organic compounds can lead to accelerated degradation. And this is the actual backside, the actual other side of the photograph that clearly shows an imprint of the board against which it was leaning perhaps for 100 years or so. So at very high concentrations, it's perfectly evident. And there are numerous examples in the conservation literature where at high concentrations, volatile organic acids or organic compounds can lead to discoloration and perhaps even mechanical decay. However, and this was a piece of research done by a PhD student of ours, we clearly, we've clearly shown that some of the, that at low concentrations or low enough concentrations of, for example, acidic acid. And by low enough, I mean 100 ppbs or 10 ppbs, the reduction in the expected lifetime of these objects is potentially entirely acceptable. Here we see for a typical rack paper, so typical paper produced between 12th century to early 19th century, we see a reduction of expected lifetime from 60,000 years to 23,000 years. It sounds like a lot. And this is, this specifically refers to the lifetime of this document in terms of discoloration, which itself we know doesn't matter too much to readers. But is this reduction of two thirds a lot, or is this something that we could live with? For example, some other documents do not show any effect of acidic acid as the most damaging pollutant in the indoor air. For example, alkaline paper degrades pretty much in the same way in the presence or absence of acidic acid as do acidic papers, for example, and papers that consist of pure cellulose. So how important is this degradation effect in terms of the overall lifetime of library and archival collections? In order to have a meaningful response to this question, we decided that we should ask the readers themselves. And it came as no surprise that the range of responses was very broad. Some readers accept a level of degradation in objects, saying that a good life of an object is indicated by signs of use, meaning that small tears or frayed edges of a document don't really matter too much because it simply means that that object has been used and therefore its existence can be justified. Others, of course, were more concerned about damage and said statements such as a bad life is indicated by signs of damage, which indicates that they have a negative attitude towards damage. But the range of these statements indicates to me that we have a very ambivalent attitude towards damage and towards decay. And that on the one hand, we like decay from perhaps a fairly romantic point of view. And on the other hand, we dislike degradation because it might mean that an object will cease to exist in the future. So in order to disentangle these issues, we conducted a large survey among readers and users of library heritage objects and were particularly interested in how long these objects need to stay in a shape good enough to be read. And with 504 responses of archival and library users, we got to the point where 90% of them were absolutely happy if documents remain in a readable state for the next 500 years. In fact, even users of mineral collections were perfectly happy with objects staying in a shape where they can be studied for the next 500 years with somewhere between 10% to 20% of those who prefer extremely long lifetimes beyond the point where there's any meaningful attitude to material decay, which as we know from a scientific point of view is entirely unavoidable. So what this tells me two things that users of heritage are not particularly concerned about what materials were preserving, whether it's rocks or paper, they have a very similar attitude to the future. And because with library and archival collections, we were specifically interested in the attitudes of readers and where we engaged geological collections users, we particularly engaged curators and expert users. It tells me that our attitude towards the future does not depend on the level of knowledge we have about preservation. It is much more deeply rooted than that. It probably reflects our attitude to the future that we can imagine. And this is typically about 100 years or multiples thereof. Why 100 years? Very probably because it represents the two, perhaps three generations ahead that we can still imagine life to have some meaningful shape that we can still imagine. So in terms of the expectations about the future, we see that all of our objects were happily survived, the long term planning threshold of 500 years, even at concentrations of the most important and the most damaging volatile organic compound, which is the acetic acid. So if that's the case, from a preservation point of view, from a preservation risk point of view, we can keep the volatile organic compounds in libraries and archives because they are typically not in concentrations that would damage them to the extent when they can no longer be kept for 500 years. So if that's the case, the preservation risk really isn't something that we should be overly concerned with, at least in the usual library and archival preservation context. So the next question that we then addressed was whether those volatile organic compounds could be used as a source of information about the state of the object. And we analyzed the number of historical papers using the so-called headspace technique, which has nothing to do with the photograph on this image. The headspace of objects is measured using this particular tool, which we call a gas chromatograph, in the way that we put a piece of paper in a glass vessel and then insert a sensor called a micro extraction needle into that glass vessel and sample the volatile organic compounds from the immediate environment of our paper object. And that immediate environment is called its headspace. It's a technique that is used by conservation scientists and heritage scientists a lot. And it allowed us to understand that different types of papers, and I'm showing chromatographic traces for four of them, really show very, very diverse concentrations of individual volatile organic compounds. And that there are potentially 10 or 15 that are contained in the aromas of most papers, such as, for example, formic acid, acetic acid, which we've already mentioned, but also others, fentanyl, hexanal, furfural, all aldehydes, but also other very interesting compounds such as two-pental furane, or furfural, which smell of burned pizza, for example, or burned bread. And many of these compounds we know are contained in other in the aromas of other similar organic materials, for example, chocolate or coffee, which isn't surprising because cellulose and lignin, the two most prominent natural polymers, natural macromolecules, are contained in those products as well, which tells me that the typical aroma of degrading paper is due to the fact that we're looking at degradation products of cellulose and lignin, and that slowly but surely cellulose will degrade by evaporation. Of course, we're going to have to wait for a very, very long period of time for that to happen to its completion, but the volatile organic compounds or the aroma of degrading paper is the slow dying breath of the material we have in front of us. What these traces also tell me is that it should be possible on the basis of the intensity of those peaks to discriminate between papers that contain more acidity and papers that contain more lignin perhaps, and that it might be possible to discriminate between papers that degrade faster and papers that degrade slower because I can imagine chemical mechanisms that will lead to the production of four for all. This is so-called hydrolysis, the most important mechanism of decay of any cellulosic product, and indeed that was the case. We tested more than 70 different real historic papers, and using a bit of statistical analysis, which we call multivariate data analysis, we were able to discriminate between papers that degrade faster and papers that degrade more slowly, and what's important on the basis of that was that we were able to identify those volatile organic compounds that could be considered as degradation markers, such as for example acetic acid or 2-ethylhexanol and some other volatile organic compounds that the human knows is also sensitive to. What's even more interesting is that we were able to identify those degradation markers that are specific for a specific component of historic paper, for example in this case lignin, a very complex molecule that's also contained in coffee and the smaller extent in chocolate, and can be contained in paper to up to 30, 40, even 50 percent. What's important, we were able to show what volatile organic compounds, aroma components can be considered as degradation markers for lignin, and therefore papers that emit more benzaldehyde, which is a particularly interesting volatile organic compounds, smelling of bitter almonds. Those papers that have a more intensive smell of bitter almonds and vanilling typically contain more lignin. What I'm talking about really is inductive knowledge generation here, because we entered this, we developed this experimental approach not really knowing what the questions are, and sometimes and increasingly so in heritage, we developed data sets where on the basis of data that we collect in the first instance, we then start generating hypothesis. This is not a usual scientific approach to discovery, this is very much an approach that is typically used in humanities and social sciences, where hypotheses are generated on the basis of case studies. In this particular approach, in this particular experiment, we first generated millions of data points on the basis of which we generated hypotheses, such as papers degrading fast, contain more lignin, and therefore the smell of vanilling. That helped us understand how chemical degradation can inform generation of smell, or can inform how we think about smell generation in decaying organic heritage materials. But at that point, we really lacked the vocabulary to describe smell. And that's where Cecilia came on board, and without her, the rest of this presentation wouldn't have been possible. In her PhD research, we started to realize that in order to understand the significance, the heritage significance of smell, we really need to develop the vocabulary to describe those smells. In order to do that, a technique exists that is often used in environmental sciences called olfactometric analysis. And we're still looking at the same gas chromatograph, except that instead of using a computer tool, a computerized tool, to detect those individual volatile organic compounds, we use Cecilia's nose to detect those compounds that have particular smells, either pleasant or unpleasant, and we use her brain to describe those smells. Namely, smells or smell vectors are the compounds that we can measure. But smell really happens in our brain because that is where we ascribe meaning to those compounds. For example, instead of benzaldehyde, we think bitter hormones. Instead of short chain aldehydes, we think, ah, the smell of dry hay. And that is the vocabulary that Cecilia developed. So instead of vanillin, the typical compound contained in lignin containing paper, we developed, we were able to name that compound and the smell that it reminds us of. Instead of short chain aldehydes, for example, propanal, butanal, etc., etc., we were able to ascribe that smell to dry hay. Instead of acidic acid, of course, we were able to talk about vinegar. And instead of benzaldehyde, we were able to talk about bitter almonds. With that language developed, we decided that we also needed a visual tool to describe the vocabulary, to visualize the vocabulary that we were developing, where in the outer circle, you see the typical compounds that I talked about. For example, acidic acid. And in the middle concentric circle, you see the, sorry, the font is a little bit small. You see the description of what that chemical compound smells like, such as vinegar, etc., etc. So for many of those really typical smells associated with decaying paper, we now not only understand what chemical compounds are contained in those smells, but we also understand how our nose and our brain interpret those smells. And we see this as an essential tool to describe smells or the posterity, the so-called aroma wheel, or historic smell aroma wheel. And we've since, or rather with Cecilia, as the lead author, we since developed a number of such historic smell wheels for different types of smells. So we can now describe a historic smell or a heritage smell, if you like, from a chemical point of view. We have the vocabulary to describe that smell. We know whether it's pleasant or unpleasant, whether it's intensive or not. We have the words to describe the individual components of those smells. But do those smells have any meaning to people? Are they really significant? What value do people put into those smells? Luckily, the Wren Library at St. Paul's Cathedral keeps a visitor book. And there is, and there are numerous examples that show how visitors appreciate the intensive aroma of that space, saying that it's even possible to inhale knowledge, which really made us think that there must be some value in the smell of objects that is important to visitors, not just of this library, but of objects more generally. But in order to assess the values that people put or project onto heritage, we needed a piece of experimental research that is often used in, say, experimental psychology or social science called factor analysis. And we know because we know that smell is used by humans almost half of the time as they communicate with their environment. This is a really interesting plot that I got from a book on advertising. Very interestingly, the advertising industry looked a lot, obviously, into how humans communicate with the environment. And while the majority of the time we obviously use our sense of sight, the second most important sense that we use in communication, while we communicate with the environment is the sense of smell, and then hearing, taste, and touch. So this really was quite revealing. It indicated to us that the sense of smell is probably used by visitors much more than we tend to think so, than we tend to think, because the majority of visiting experiences in museums and galleries have been reduced to the sense of sight. So if smell is so important, does it feature in how people value library and archival collections, for example? In order to do this piece of research, we had to engage a large number of readers and visitors, for example, to the National Archives in the UK, the Library of Congress in Washington, to English Heritage properties visitors, as well as the Capital Visitor Center in Washington, obviously, as well and in the National Archives Museum in London. And we asked them a range of questions about how they value objects. And among those statements was one statement that also highlighted the value of smell. It's really interesting that this particular statement featured in one factor or in one value, as we later described it, that was typically associated with the material aspect with the material properties of the document. And we called this value the material value of objects. Of course, the majority of visitors in libraries and archives are concerned with the content of objects, such as, for example, objects are important because they will be valued by people in the future, because they are in a library that's existence value, obviously, because someone thought it was worth creating, because such objects are important economic resources or such objects gives me insight into my personal origins. These are all values associated to the textual content of library and archival objects. But the one value that really focuses on the material evidence in front of us really strongly relies on the sense of smell or on the smell of the object, which tells us that smells are an important way of how the typical user, the typical reader in a historic archive or in a historic library interacts with the book or with their archival object. There's obviously commercial value of smell as well, as indicated by the numerous products that can be purchased on the market. And there are numerous, obviously, scented candles that purport the smell of historic libraries and even perfumes that people that are being sold to avid book readers and apparently even an air freshener that smells of freshly printed books. So there's evidently a commercial opportunity there as well, but is there value in smell as heritage, apart from what our readers and users of historical libraries think? Not yet, I would say. There is just one convention, heritage convention, that mentions smell in passing. It is the Barra Charter where it says that the value of a place may include sensory aspects of the setting, such as smells and sounds. So although we've come to see the commercial value of historic smells, although we've come to understand how our visitors to heritage spaces and historic libraries value the smells of those environments and of those objects, that yet has to be recognized in heritage charters. It is, however, already recognized in various activities and various recognitions that all factory heritage has already received. For example, the city of grass has been confirmed as a World Heritage Site based on the perfumes and the knowledge of perfume making that pervades this city and its history. And some of you may know that in Japan the national route through the best 100-cented sceneries has been established. Based on a large piece of research that included the public, those scented sceneries include obviously cherry orchards, but also other places of intensive smells, such as, for example, fermented fish factories, because we identify ourselves also through the smells of our environments. We deeply remember the smells that we have learned in our childhood and those define our culture as well. At the end of this presentation, I'd really like to invite you to follow two of the projects that we are still active in, where we explore the value of smell as heritage, Cecilia's smell of heritage project, as well as a new project that we're starting in European Union, the ODE Europa project, where we'll be looking at smells and the value of smell in historical narratives and even trying to reproduce some of those smells to be used in historic displays and exhibitions. I hope this was of interest and thank you very much for your attention, and I'm looking forward to our discussion. Thank you. Thank you, Mattia. Give us a second to turn on our screens. Wonderful presentation, really terrific. I enjoyed every bit of it, so I'm looking forward to the discussion, and I want to make time for people to get themselves organized a bit to ask their questions. I'm going to invite everyone to start your video, where we can have a nice conversation, all of us more in-person, so please go ahead and do that, and I will try to do that myself, although I find myself having trouble, and maybe others are having the same issue, but here we go. I think, yeah, finally I was able to do that. Go, yes. So, Mattia, maybe I'll just get us started, and I hope that others will go ahead and turn on their screen, and we can have a conversation that way. But I was really struck by the way in which your work has opened up, let's say, the realm of activity of the, the traditional realm of activity of the conservator. So I was struck, for example, by your openness to include methods of research that really are drawn from the social sciences into your work, and maybe this is what makes you an unusual scientist, because there is a great deal of discomfort, I think, in the traditional, you know, conservation science world, in doing that, because I think it, well, I'm curious to hear from you, actually, rather than me speculating on it. I'd love to hear from you, your speculation as to why you decided to move in that direction, the need you felt for that. You did introduce it to us in the discussion of values, that you decided to move into the realm of social science and environmental psychology, which made me think that there was a kind of tacit understanding of science as value-less. In other words, that when you're dealing in the science world, you're not in the realm of values, but in order to move into the realm of values, you have to move into the humanities, which I think we might question, and we might explore that a bit more, and I would love to hear. Sure. Yes, that's a very good observation, Jorge. I must say that when I questioned my role in conservation or in conservation science or heritage science, as we've come to call it, and as I questioned what heritage science is, I started to think that what makes it really different from any other domain or discipline, if you like, is that it constantly and consistently needs to involve or needs to take, needs to consider is the value of the object, and by object I mean really just any typology of heritage in front of us, because any work that we do on heritage will change its value. Look at, for example, the work that's been done on say Van Gogh's Sunflowers, all of the science work that's been done contributed to an increased value because people now want to see the object even more. So whether or not we want it, our work as scientists impacts the value of objects that we consider. And on the other hand, heritage is a subject of research that is defined through its value. Therefore, we must understand how value features in the research or the science that we do, and that involves that heritage. So I really, really wanted to understand how value of objects can be assessed, if not measured even, and I was really, really pleased to get to know of techniques that are used in social science and that enable us to do so. Of course, we have a number of techniques in anthropological research or ethnographical research that are based on interviews and similar techniques. But I really wanted to see whether there are techniques available that enable us to do that a little bit more quantitatively, because I am a quantitative scientist after all. So I think we, as heritage or conservation scientists, we absolutely cannot not consider values in our research, either as a research subject of their own, or in terms of how our work affects the value of those objects. Thank you for that. I see Emily Spratt has a question. Hi. Thank you so much for the presentation. And my internet connection is a little wonky, so I'm going to leave my video off. I apologize. My question was actually more in regard to potential applications of the work that you have done. Would it be possible to develop a sensor that could actually be placed in libraries to form as a kind of early detection system for the potential over degradation of manuscripts, for instance, so that then there could be kind of an alarm, an early alarm for conservators to then go in and be able to help with things before they deteriorate too much? And on the other side of that, I was very interested by your mention of the Burra Charter and was wondering if you could also maybe in an outdoor environment develop a kind of sensor for detecting pollution for, let's say, a temple that has marble, which is vulnerable to degradation. And if it happens to be near a factory, for instance, could there be a sort of monitor for high pollution levels? I think that this would fit very well with UNESCO's objective right now of thinking in a larger way about sustainability and environment and the connection of a site to the larger environment. And I see smell and the detection of smell as being a wonderful way to actually make that relationship more visible and possibly to help with monitoring it. That's a great question, Emily. Thank you so much or a couple of questions, really. I think in terms of your first question, whether or not it might be possible to develop sensors to detect objects that degrade past or faster than others, yes, this is entirely possible and such sensors actually do already exist, but they are, A, too expensive and B, too power hungry to be used on a large scale. Ideally, I think it would be amazing to have such sensors say in each box where an object is stored, and if there is a sudden burst of smell or volatile organic compounds in the microenvironment of that object, that would be an indication of an onset of rapid degradation. So in principle, that is what you asked is already possible, but it is that technology is currently prohibitively expensive to be used on a large scale in conservation. Just one interjection on that point. I know that NASA has actually been very active, especially recently, in making more accessible their research and developing partnerships. And I know that there's been a lot of work done actually in the context of the space stations to making, monitoring those spaces to make sure that smells, air quality, all of those things are, you know, of course, like in a very detail oriented way, absolutely perfect for our astronauts. So I wonder actually if there couldn't be a potential partnership further down the road with that, since you're already collaborating with such interesting groups of people. You're absolutely right. Where there is most development in this field is actually detection of explosives. So military industry, as well as in health industry, because through breath analysis, it is possible to detect certain illnesses in people. And sensors exist that show you whether or not on the basis of volatiles in your breath, there is an indication of cancer development, for example. So technologies are there, but it still isn't imaginable to have, say, 10,000 or 100,000 of such sensors in a library environment or in a storage environment. As to your second question, in terms of detection of pollutants and detection of volatile compounds in historic spaces, that has been done in the past. There are however few degradation processes where particularly volatile organic compounds in outdoor environments are a risk or are seen as a particular risk. Yes, nitrogen dioxide or ozone and similar traditional traffic generated pollutants are typically considered a risk and sensors exist for those and are also inexpensive. But volatile organic compounds and their effect on even highly polished marble surfaces, for example, that you mentioned, the effect of those is much less well understood. So there is a little bit of research that still needs to be done. Thank you so much. My understanding was that the cancer detection breath tool was actually based upon technology that was developed at NASA with the space sort of station. So I think that NASA really does still even for potential breath health and also military things. In what I have researched so far, actually NASA really is sort of the originating point for that. So again, I still think that could be a potential collaboration opportunity for you. But thank you so much for all your answers. Oh, no, no. I mean, you evidently know NASA technologies much better than I do. I work with a couple of companies based in Europe and it's entirely possible that their technologies are based on a previous NASA development. So I don't know that deep history as it may be. Other questions that if anybody has a question, please feel free to jump in. Make a little bit of time for that. I think people are a little shy here. I was maybe I'll take it as an opportunity to jump in and let people think about if they have their question just you can type it in the chat or you can just raise your hand or what have you. But I was curious about the question of meaning that you brought up in relationship to smells. And the naming of the naming wheel, which of course one can see the relationship between that naming wheel and the one used by perfumers to try to basically analyze smells and break down smells into their components. And many of those, sorry, apologies, many of those wheels have to do of course with organic compounds, but I was very pleased because flowers and so on are used in perfumery, but I was very pleased to see that you had also inorganic materials in there and the smell of coal and other pollutants in the air, which I thought is really terrific. And that one, the smell of coal really made me think about this question of meaning because if you travel, for example, to Istanbul or to Ankara, especially Ankara, you're really struck by the smell of burning coal. It is an open burning of coal in people's houses for cooking or for heating is very common. The government distributes it at a subsidy because it's the cheapest fuel that they have. And so it is a very special smell that you find in Ankara, but you don't find in other cities. You don't find it in New York because we don't burn coal in the city. We burn it in factories and the smoke is heavily processed and let's say cleaned up through various techniques. But there is a kind of association to place with each of those smells. And there's a particularity of smelling coal in Ankara that is very different than smelling coal somewhere else. So I guess I'm wondering about as a long-winded way of asking about heritage places in relationship to that heritage wheel and meaning. Because one immediately wonders, what is the intended outcome of describing the smell? When you're talking about a material, you're trying to identify either it as a character defining feature of the building that you are calling for its preservation through some sort of regulation or you're assessing its condition of degradation and calling for some kind of intervention of conservation. It seems that the ladder is actually not really an option in terms of or maybe it is in terms of smell conservation. In other words, you can identify the smell through the through the smell wheel to call it out as a character defining feature, but not to stabilize it or conserve it in any way. I think you opened a range of issues here and this really requires a longer conversation, I think, which I'd be absolutely happy to have. And it really touches upon some of the conversations that we're having about the significance and meaning of smell and to whom. Because smell is so contextual, as you pointed out. The smell of burning coal for me is complete nostalgia, because that's what I smelled when I was 10 years old and I'm sure that if I travel to Ankara today, I would be taken back to my childhood immediately. But to someone else, it's just an awful, acrid acidic smell. And the smells of their childhood are potentially completely different. The smell of my childhood is potentially involves the toys that I played with, but the smells of children born perhaps 10 or 15 years after me are associated with play, though, that means nothing to me. So smell as well as its meaning is entirely contextual and it is temporal as well. What I mean about contextual is that it depends that our interpretation of a smell, of olfactory information, depends very much on the environment in which we perceive that smell. For example, the same compound, geosmin, means the smell of a decaying moldy surface if we are in the cellar of a building. But exactly the same compound, if you're outdoors in a forest, means the smell of autumn environment. And the two are chemically completely the same. But because of the context in which we perceive those chemicals, one of them is negative and the other one is a very positive smell. How do we capture that in terms of significance is a big question. On the one hand, we need to have the tools to describe those smells, which is where the smell wheel comes in. And in some industries, for example, food industry or perfumery, and even environmental industries, they developed those wheels already. And some of the language that I read on the back of a wine bottle means absolutely nothing to me, but it means a lot to people who understand about wine aromas. And we want to develop the same for historic objects as well, so that we understand each other as we discuss smells of historic objects. But also we must have a way of describing smells that will be meaningful to people in the future if we want to preserve those smells. And we need to preserve the language and also we need to preserve what those smells mean to us, meaning the significance. We need to be able to describe the context in which those smells are perceived today and the meaning to whom as well. And that requires a significance assessment that we sometimes do for other forms of heritage, for example, buildings. And as buildings get listed, for example, or as sites become World Heritage Sites, those significance assessments become quite thick documents, because we need to consider all of the same issues, i.e., what's the value of that building to whom, when, what element, etc., etc. So we need to develop exactly the same for smells as well if we want to consider them as heritage objects in their own right. We then, of course, need to have a way of measuring those objects, a way of quantifying those smells. And as chemists, we have the tools at hand to do so. And thirdly, we need to find a way to reproduce faithfully or authentically, if you like, those smells in the future. And that's an aspect that we are struggling with a little bit at present, and that we're doing research into. Fascinating, thank you. It's so interesting what you say in terms of if you apply that, all those, all those complications about, for example, the ability to reproduce it to material heritage, right? If you were to say, you can't materially replace a column, you know, how does that cascade back to the significance assessment, you know, that it would call into question a lot of the ways in which we assess significance if we couldn't reproduce it in its documentation. You're absolutely right, but the fact is that we do reproduce it, you know, rarely, but we do. Although from a material point of view, it's not the authentic column, but it may fulfill the same function both, you know, architecturally and aesthetically. And in fact, in, as I'm sure, you know, in some cultures, conservation is not about the materiality of the object. It's about what it represents in various cultures in Eastern Asia, for example, the materiality of an object has very little meaning. And the authenticity is in the fact that we can build such an object. The Shinto shrines in Japan, for example, are rebuilt every 30 years. And it's not the material shrine that is valued, but the fact that we can rebuild them and use them again. I see Miguel Fauci has a question. Miguel, go ahead. Oh, hi, thank you so much for such an inspiring talk. And I was wondering exactly what you just said about Japan, because there's something very interesting. As you were talking, I was wondering, because in the West, usually the buildings, the smells that we sense in our buildings, they come from the objects, whereas in Japan, because most of the, or these historical buildings were made out of wood. So we smell that wood. And it's interesting because of the approach to heritage. These wood would always be like fresh wood, right? Because they would rebuild it every 20 years. So I was always wondering, like for example, the kind of trees that they are using to rebuild their shrines and everything. The smell will change, right? And then I'm wondering, what are you preserving in terms of smell? Are you preserving like always the freshness of that cut wood? Or are you preserving actually the atmosphere because it comes with this incense and all the other smells that are in that shrine, right? So it made me think a lot about these issues. You opened a really interesting area of research, I think, with this question. And obviously the answer needs to be depends on what we find of significance. If the smell of fresh wood is what is significant to people, to visitors, then that perhaps should be preserved. If it's the smell of decaying wood, then that needs to be preserved. This brings me to some of the examples that we discussed recently where, for example, an archaeological vessel was preserved in a way that it was consolidated and then varnishes were applied, etc., etc. So the authentic archaeological vessel that contained food changed its smell to something completely artificial, but it would be wrong of us not to consider the current smell of that vessel as inauthentic. It's just a different smell of that same object in a different period of time, same as with books. Books, when printed, have a very different smell to the smell of decaying books a hundred years on. And I'm sure that significance assessments could be developed for both moments in time for the same object which really questions how we understand authenticity, doesn't it? Absolutely. Thank you, Matilla. I think we've kept you way over our time, but it's just such a fascinating topic and such fascinating work that we couldn't help ourselves. So I just want to again thank you so much for sharing your knowledge and your work with us, and we leave this presentation so much richer with all these new ideas. So much appreciated. I hope you'll join us again in the lecture series or in the program soon and when you come through New York. But thank you everyone. Again, I'll do the clapping for everybody else. So thanks Matillian.